Article: Jet lag

Jet lag, also jetlag or jet-lag, is a physiological condition which is a consequence of alterations to the circadian rhythm. Such alterations result from shift work, altered day length, or as the name implies, transmeridian travel as on a jet plane. They are known as desynchronosis, dysrhythmia, dyschrony, jet lag, or jet syndrome. The condition is generally believed to be the result of disruption of the "light/dark" cycle that entrains the body's circadian rhythm. It can be exacerbated by environmental factors.

Causes

When traveling across a number of time zones, the body clock goes out of sync with the destination time, and so it experiences daylight and darkness contrary to the rhythms it has grown accustomed to. The body's natural pattern therefore becomes upset as the rhythms which dictate when you should eat and sleep no longer correspond to the environment of your destination.

Jet lag occurs because the body cannot automatically realign these rhythms. The speed at which the body readjusts itself to new daylight, darkness hours, and eating and sleeping patterns is entirely dependent upon the individual. Thus, while it may take a few days for certain people to readjust to a new time zone, others seem to experience little disruption to their body's natural sleeping pattern.

The symptoms of jet lag can be quite varied, though on the whole, an individual may experience the following:

• Dehydration and loss of appetite
• Headaches and/or sinus irritation
• Fatigue
• Disorientation and/or grogginess
• Nausea and/or upset stomach
• Insomnia and/or highly irregular sleep patterns
• Irritability, Irrationality

Dr Neil Stanley, past chairman of the British Sleep Society, sounded (4/2006) a note of warning over jet lag due to large time differences. He said: [1]

If you are frequently changing time zone or working long hours or shifts, you do start working at only 60 to 70% of your potential. You lose concentration, you lose judgement, you lose reaction - so [e.g.] as a politician you are not going to be on top of your game, to be honest.

The maximum jet lag a person can experience is 12 hours. If the difference in time between two places is greater than 12 hours, subtract that number from 24. For example, there is a 16 hour time difference between Los Angeles, California (standard time) and Hong Kong. Thus, 24 − 16 = 8 hours of jet lag. The person will incur the same amount of jet lag as someone traveling between London and Los Angeles, where the actual time difference is 8 hours. Disregard the difference in date if flying across the International Date Line.

The condition is not linked to the length of flight, but to the transmeridian (i.e. East-West) distance traveled. Hence a ten-hour flight between Frankfurt and Johannesburg is less inducive of jet lag than a five-hour flight between New York and Los Angeles. There is no firm agreement as to which direction of travel is worse. Some believe that traveling east is worse as it "accelerates" the passage through various time zones (a night might only last 3 hours when flying east), and because the symptoms of traveling west, such as waking earlier in the morning, can be easier to integrate with ordinary life. Others counter that the impact is worse when one travels away from one's "habitual" time zone, and is minimised when returning to it.

Although technically incorrect, the term jet lag is sometimes used in conversation to describe the general exhaustion of traveling, even if there is no change in time zone.

Prevention and recovery

Simple prevention can be good sleep aboard, and adequate intake of fluids (without coffee or alcohol) to reduce the effects of dehydration on the body, caused by the dry air at altitude and the interruption of regular eating/drinking patterns. Seasoned travelers set their clock to the destination time zone, as soon as it is practical, and join the new rhythm. Exposure to sunlight may be a factor to reset the body's clock. For people who do not fly multiple times per week, it can be an effective non-drug remedy to skip sleep entirely for one night and one day and then go to bed at a normal destination-area bedtime on the next day.

Recent research shows that the pineal hormone melatonin may reduce the effects of jet lag. Studies have not identified side effects from such short-term use. [2] Many products on the market claim to treat the effects of jet lag. Since the experience of jet lag varies among different individuals, it is difficult to assess the efficacy of any single remedy. In addition, most chemical and herbal remedies are not tested or approved by the Food and Drug Administration, therefore their safety has not been scientifically established.

The condition of jet lag generally lasts a few days or more, and medical experts have deemed that a recovery rate of "one day per time zone" is a fair guideline. Sleep, relaxation, moderate exercise, and sensible diet seem to be the simplest recovery agents.

Good sleep hygiene promotes rapid recovery from jet lag.